But they don't make it clear that it is not available on 90% of the books. And, while you can see if a particular book has X-Ray enabled or not, you cannot figure out whether it is useful or not - the quality really varies from book to book.

I buy alot of books and none of them have had the feature yet. But i love the idea of x-ray for fiction, so i could refresh my memory for minor characters, etc it sounds easier than using search.